**3.2 Insecticide resistance to neonicotinoid**

Resistance is quickly developed due to the selection of highly effective compounds with kill or mitigate to insect, long residual effect, and is regular use of single biochemical target site. The toxicant is converted into a nontoxicant form in the body of an insect by various enzymes. All these enzymatic changes are carried forward and transmitted through genes. Resistance in B- and Q-type has been noticed in *Bemisia tabaci* to enhanced oxidative detoxification of neonicotinoids due to overexpression of monooxygenases. No evidence for target-site resistance has been found in whiteflies [18, 19]. Biotic and abiotic degradation processes contribute to the environmental persistence of neonicotinoids. The half-life of neonicotinoids varies depending on physiochemical

**Figure 2.**

*Several reported cases of neonicotinoid resistance up to 2014. Only those pests with >10 (fold) reported cases are shown.*

#### **Figure 3.**

*Pesticide resistance can build up in the pest population when a change in the genetic characteristic of the pest population is inherited from one generation to the next.*

conditions (i.e., organic matter content, soil texture, residence time) before undergoing complete degradation. The development of resistance is a complex and dynamic process and depends upon many factors. As per the IRAC, resistance is well-defined as a heritable change in the sensitivity of a pest population, that is reflected in the constant failure of a product to attain the expected level of control when used according to the label endorsement for that pest species [20]. The environmental protection agency (EPA) is divided into two classes of toxicity agents i.e., II and III. Accumulation (increase the level of pesticides) of those pesticides into the soil affects the pollen quality of sprayed plants, especially due to their toxic effects, against pollinators the consequences of the occurrence of these insecticides have been discussed [10, 21]. It is determined that the transfer of vertical gene (a particular gene) from the microorganism, higher plants, animals into a host plant for crop improvement and researches are called transgenic plant or insects, virus, fungus resistance plant. It gives us facts for future research. Mutation (can build up in the pest population when a change in the genetic characteristic of the pest population is inherited from one generation to the next) in nAChR subunits and in most cases, metabolism is also responsible for the development of resistance (**Figure 3**). The brown planthopper, *Nilaparvata lugens*, was selected with imidacloprid treatment at a sublethal dose to obtain resistant mutation. Both *Bemisia tabaci* (sweet potato whitefly) and *Trialeurodes vaporariorum* (greenhouse whitefly) have been shown to have a high possibility for resistance development and characterize some of the main targets for which IRAC specific strategies have been developed [8, 22]. Global resistance management guiding principles were designed by the Neonicotinoid Working Group of the Insecticide Resistance Action Committee and are based on guidelines published and updated earlier [9].

## **4. Mechanism of resistance and factors that influence resistance development**

#### **4.1 Resistance mechanisms**

The various mechanisms that enable insects to resist the action of insecticides can be grouped into several categories:

*Insect Resistance to Neonicotinoids - Current Status, Mechanism and Management Strategies DOI: http://dx.doi.org/10.5772/intechopen.101129*

#### *4.1.1 Single resistance*

Resistance to Dichloro diphenyl trichloroethane (DDT) amounts to resistance to several DDT analogs such as methoxychlor, but not to hexa chloro cyclohexane (HCH). Due to excessive and continuous use of the insecticides.

#### *4.1.2 Cross-resistance*

It occurs when resistance to one insecticide or within a group. Eg: organophosphate insecticides, fungicides etc.

## *4.1.3 Multiple resistance*

It involves multiple, independent resistance mechanisms, which often lead to resistance to chemicals from different families (i.e., organophosphate and carbamate insecticides) [23].

#### *4.1.4 Metabolic resistance*

It plays one of the significant roles, in the development of resistance which helps to change the activity of enzyme systems that all insects possess to help them detoxify naturally occurring foreign materials. Enzymes are classified viz., esterases, monooxygenases, and glutathione S-transferases typically fulfill this function. These enzyme systems are often enhanced in resistant insect strains enabling them to metabolize or degrade insecticides before they can exert a toxic effect. Metabolic resistance appliances have been noticed in whitefly, aphid, and Colorado potato beetle populations for all major classes of insecticides, currently also used for soft body insect control including neonicotinoids insecticide [24].

#### *4.1.5 Target site resistance*

Insecticides generally perform on a specific site within the insect, especially within the nervous system (e.g., OP, carbamate, and pyrethroid insecticides). The site of action can be reformed in resistant strains of insects such that the insecticide no longer binds effectively. This results in the insects being unaffected, or less affected, by the action of insecticide than susceptible insects.

#### *4.1.6 Reduced penetration*

Changes in the insect cuticle or digestive tract linings that avoid or slow the absorption or diffusion of insecticides can be found in some strains of resistant insects. This resistance mechanism can affect a broad range of insecticides. Examples of reduced penetration mechanisms are limited and are often considered a contributing factor to reduced susceptibility.

#### *4.1.7 Behavioral resistance*

This resistance illustrates any adjustment in insect behavior that helps to avoid the lethal effects of insecticides [22]. Insecticide resistance in mosquitoes is not always based on biochemical mechanisms such as metabolic detoxification or target site mutations, but may also be conferred by behavioral changes in response to prolonged exposure to an insecticide.


#### **Table 1.**

*Mechanisms of neonicotinoid resistance and tolerance in insects.*

## *4.1.8 Genetic basis of resistance*

It occurs naturally, genetic mutations allow a small proportion of the population to resist and endure the effects of the insecticide. This occurs due to continually using the same insecticide and horizontal genes. Resistance insects will reproduce and the genetic changes that confer resistance are transferred from parents to offspring so that eventually they become numerous within the population (**Table 1**).
